30. maaliskuuta 2017

Thanks for attending yesterday's endgame tournament. The goal of these is to improve our overall chess skills. The endgame is often underestimated for its importance even though the difference between winning and drawing can be a matter of just a single seemingly innocuous error.

You have the opposition if there are an odd number of squares between your king and opponent's king on the same file, and it is his turn to move. The aim of having the opposition is to penetrate. So once the opponent is forced into a weak square, you should step sideways and forward – this is known as outflanking.

Edmar Mednis gave this breakdown when the defending king is not able to help:

A bishop pawn is the best pawn to have. It is relatively easy to advance and is a win once it reaches the seventh rank.

A central pawn wins if it reaches the seventh rank, but it is difficult to get it there. Even if the pawn reaches the sixth rank, the position is usually a draw.

A knight pawn is relatively easy to get to the seventh rank, but the position may be a theoretical draw.

Positions with rook pawns are theoretical draws, but in practice it may be difficult to draw (Mednis 1987:126–27, 134).

John Nunn gives this summary for the defense:

With a central pawn, the defense has two possibilities: get the king in front of the pawn or get the king to corner nearest to the pawn's promotion square.

With a bishop pawn, the defender's only chance is to get the king in front of the pawn.

With a knight pawn, the defender must get the king in front of the pawn or in the corner furthest from the promotion square.

A rook pawn is generally a draw and the defensive guidelines are the same as for a knight pawn.

Queen vs Queen + Rook Pawn

In 1985 the chess computer Belle completed the endgame tablebase for this ending. The rook pawn is the most important for actual games since it arises the most frequently, since it is the least likely pawn to have been exchanged (Mednis 1996:93). A rook pawn needs to be on at least the sixth rank to have decent winning chances (Nunn 2007:150).

Mednis gave these guidelines, based on his analysis of the tablebase. Assume that White has a pawn on the h-file.

To draw:

The best area for the king is in the corner opposite the pawn's promotion square. This keeps it from blocking checks by its queen.

When the white queen is centralized, the safest place for the black king is probably b3.

Once the king is in the far corner it should stay there.

At certain points the king can be on other squares and still draw, but it is much more difficult to play correctly.

The queen should be centralized.

The queen checks on the central squares for more flexibility on future moves.

The queen checks in ways so that the white queen cannot be centralized.

The queen is used to keep the king in front of its pawn.

The queen is used to prevent the white queen from becoming active.

If the queen is on e5, it will draw against a pawn on h7 and queen on g6 or f7 if the black king is in the far corner.

The queen is kept active and in a flexible place. It will be more active on c2 than h7.

The queen on h7 is often good enough to draw.

To win:

The worst place for the king is in front of the pawn.

There are two good places for the king:

to the side of the pawn; e.g., f7, f8, or e8.

close to the black king, which allows for counterchecks.

The pawn is advanced to the seventh rank only if the queen is in place to prevent perpetual check.

If the pawn is on h7, the best square for the queen is e4. In favorable circumstances, other squares (e.g. f5, d7) will also win (Mednis 1996:115–17).